Asthma is a major health problem in this country. Intrapulmonary allergen challenge in asthma induces a "late phase asthma phenotype," consisting of airway hyperresponsiveness (AHR), airway mucus production, and Th2 eosinophilic inflammation. A large body of literature has dissected out how peptides and epitopes of pollen-derived antigenic proteins interact with critical components of the adaptive immune system namely Class II MHC on antigen presenting cells, and T-cell receptor on Th2 cells, to induce late phase asthma phenotype. However, it has never been shown that pollens contain a second set of protein(s) with unique biochemical properties that vigorously augments late phase asthma phenotype. Ragweed pollens are known to induce allergic rhinitis and asthma in humans. We discovered that ragweed extract (RW) and many environmental pollen extracts contain potent pro-oxidant activity. Using RW as a prototypic pro-oxidant allergen, we demonstrated that this activity was due to a protein complex consisting of several distinct Pro-Oxidant Proteins (POP) tightly associated with Amb A1 (antigen E), the major antigenic component of RW. We coined a term" Pro-Oxidant Protein and Antigen Complex, (POPAC)" to describe this POP + antigen protein complex. Purified Arab A1, unlike whole RW or Amb A1 complexed in POPAC, did not possess pro-oxidant activity. Consistent with this difference in pro-oxidant activity, intrapulmonary challenge of sensitized mice with POPAC, but not Amb A1, potently induced allergic inflammation. We propose that RW (and many other pollen and mold allergens) contains POPAC, a protein complex of at least two physically associated components, the well-known antigenic component, and a novel POP. The overarching goal of this proposal is to determine the mechanism by which POP vigorously augments the late phase asthma phenotype induced by the antigenic component of POPAC. In this proposal, we will test the hypotheses that POPAC-induced immediate oxidative burst is independent of allergic sensitization and adaptive immunity (specific aim 1), and that pro-oxidant proteins augment allergic sensitization and antigen-induced late phase AHR, mucin production and Th2 allergic inflammation in mice (specific aim 2), pro-oxidant activity of RW augments immediate ROS production and late phase symptoms, mucus production and Th2 allergic inflammation in atopic patients (specific aim 3). These studies are designed to elucidate a novel paradigm of late phase asthma phenotype that is initiated by pro-oxidant protein complex (POPAC) present in many environmental pollen and mold allergens. Future studies of POPAC may identify novel therapeutic approaches in asthma.